L 8 equalization and proportioning

LLLL----8888

EQUALIZATION EQUALIZATION EQUALIZATION EQUALIZATION AND AND AND AND PROPORTIONINGPROPORTIONINGPROPORTIONINGPROPORTIONING

Industrial Waste Treatment

Equalization

�Industry will always realize benefits from delivering a constant quantity and quality of waste from its plant.

�It will further benefit from �It will further benefit from delivering this waste in proportion to that occurring in its discharge environment—be it river or sewer line.

�The reason for these facts is that receiving environments can always cope better with a constant load of contaminant and in proportion to its own existing load.

�In fact, an industrial plant can �In fact, an industrial plant can sometimes can decide not to do any further expensive treatment of its wastes after equalization and proportionment.

�Equalization is a method of retaining waste in a basin so that the effluent discharged is fairly uniform in its water quality uniform in its water quality characteristics (pH, color, turbidity, alkalinity, biochemical oxygen demand [BOD], and so forth).

�The influent to an industrial wastewater treatment system (IWTS) varies in flow and concentration of pollutants because the discharges from the manufacturing and utility processes are not constant.

�This variation affects the operation of the IWTS and could adversely affect the the IWTS and could adversely affect the effluent quality from the plant.

�The objective of equalization is to minimize or control fluctuations in wastewater characteristics in order to provide optimum conditions for subsequent treatment processes.

�In-line and side-line equalization systems are both effective ways to equalize flow volumes, but in-line equalization is more effective for leveling out the variations in influent concentration because the entire flow is blended with the entire flow is blended with the entire contents of the holding tank.

�The size and type of equalization basin provided varies with the quantity of waste and the variability of the wastewater stream.

�The basin should be of a sufficient size to adequately absorb waste fluctuations �

to adequately absorb waste fluctuations caused by variations in plant-production scheduling and to dampen the concentrated batches periodically dumped or spilled to the sewer.

Objectives of Equalization

1.To provide adequate dampening of organic fluctuations in order to prevent shock loading of biological systems.

2. To provide adequate pH control or to minimize the chemical requirements necessary for neutralization. necessary for neutralization.

3. To minimize flow surges to physical-chemical treatment systems and permit chemical feed rates compatible with feeding equipment.

4. To provide continuous feed to biological systems over periods when the manufacturing plant is not operating.

5. To provide capacity for controlled discharge of wastes to municipal discharge of wastes to municipal systems in order to distribute waste loads more evenly.

6. To prevent high concentrations of toxic materials from entering the biological treatment plant.

�A secondary but significant effect is that of lowering the concentration of effluent contaminants.

�This is accomplished not only by discharging out the slugs of a high discharging out the slugs of a high concentration of contaminants but also by physical, chemical, and biological reactions that may occur during retention in equalization basins.

�Air is sometimes injected into these basins to provide:

(1) better mixing;

(2) chemical oxidation of reduced compounds;

(3) To achieve Some degree of biological oxidation; and

(4) agitation to prevent suspended solids from settling.

Equalization tank

Equalization tank

Equalization tank

�The mere holding of waste, however, is not sufficient to equalize it. Each unit volume of waste discharged must be adequately mixed with other unit volumes of waste discharged many hours previously.

�This mixing may be brought about in the �This mixing may be brought about in the following ways:

(1) proper distribution and baffling;

(2) mechanical agitation;

(3) aeration; and

(4) combinations of all three.

�Proper distribution and baffling is the most economical, though usually the least efficient, method of mixing. Still, this method may suffice for many plants. Horizontal distribution of the waste is achieved by using either several inlet pipes, spaced at regular intervals across pipes, spaced at regular intervals across the width of the tank, or a perforated pipe across the entire width.

�Over and- under baffles are advisable when the tank is wide because they provide more efficient horizontal and vertical distribution

Baffled equalization tank

�Mechanical agitation eliminates most of the need for baffles and generally provides better mixing than baffles alone. One typical arrangement, shown in Figure , uses three wooden gate–type agitators spaced equidistantly along the center line spaced equidistantly along the center line of the length of the tank. Agitators operated at a speed of 15 rotations/min (rpm) by a 3-horsepower (hp) motor are usually adequate.

Mechanical Agitators

Proportioning

�Proportioning means the discharge of industrial wastes in proportion to the flow of municipal sewage in the sewers or to the stream flow in the receiving river.

� In most cases, it is possible to combine equalization and proportioning in the �

equalization and proportioning in the same basin.

�The effluent from the equalization basin is metered into the sewer or stream according to a predetermined schedule.

��The objective of proportioning The objective of proportioning in sewers is to keep constant the percentage of industrial wastes to domestic sewage flow entering the municipal sewage plant. This procedure has several purposes:

(1)To protect municipal sewage treatment using chemicals from being impaired by a sudden overdose of chemicals contained in the overdose of chemicals contained in the industrial waste;

(2) To protect biological-treatment devices from shock loads of industrial wastes that may inactivate the bacteria; and

(3) To minimize fluctuations of sanitary standards in the treated effluent.

Methods of proportioning

There are two general methods of discharging industrial waste in proportion to the flow of domestic sewage at the municipal plant:

1. Manual control related to a well 1. Manual control related to a well defined domestic sewage flow pattern, and

2. Automatic control by electronics.

�Manual control is lower in initial cost but less accurate.

�It involves determining the flow pattern of domestic sewage for each day of the week over a period of months.

�months.

�Usually one does this by examining the flow records of the sewage plant or by studying the hourly water-consumption figures for the city.

�Automatic control of waste discharge according to sewage flow involves placing a metering device that registers the amount of flow at the most convenient main sewer connection.

�This device translates the rate of flow in the sewer to a recorder located near the the sewer to a recorder located near the plant’s holding tank. The pen on the recorder actuates either a mechanical (gear) or a pneumatic (air) control system for opening or closing the diaphragm of the pump.

�There are, of course, many variations of automatic flow-control systems. Although their initial cost is higher than that of manual control, they will usually return the investment many times by the savings in labor costs.

Objective Questions

1. ________________ is a method of retaining waste in a basin so that the effluent discharged is fairly uniform in its water quality characteristics .characteristics .

2. For better mixing of wastewater, _____is sometimes injected into equalization basins .

3. The objective of The objective of __________________ __________________ in sewers is to keep constant the percentage of industrial wastes to domestic sewage flow entering the municipal sewage plant.

4. In case of proportioning, ________ control is lower in initial cost but less accurate.

5. In equalization, ____________ agitation eliminates most of the need for baffles

Theory Questions

Q1. Write Short notes on

i. Equalization

ii. Proportioning

Q2. Explain in detail ‘Equalization Q2. Explain in detail ‘Equalization and Proportioning’.

Q3. Explain the terms

1. In-line Equalization

2. Side line Equalization